IN VITRO AUTORADIOGRAPHIC ENDOTHELIN-1 BINDING SITES AND SARAFOTOXIN S6B BINDING SITES IN RAT TISSUES

SUMMARY 1. The distribution of binding sites for [125I]‐labelled endothelin‐1 ([125I]‐ET‐1) and [125I]‐labelled sarafotoxin S6B ([125I]‐SRT) was visualized in rat tissues using in vitro autoradiography. 2. A high density of endothelin‐1 (ET‐1) binding was found in the heart. In the kidney, ET‐1 binding occurred in association with glomeruli, proximal tubules, the inner stripe and inner medulla. In the adrenal, a high density of ET‐1 binding occurred in the medulla as well as the zona glomerulosa. 3. The binding affinity constant (KA) for ET‐1 binding in these sites ranged from 1 to 10 X 109/mol per litre. 4. Although sarafotoxin S6B (SRT) was 10–100‐fold weaker than ET‐1 in displacing [125I]‐ET‐1 from these sites, 1 μmol/L unlabelled SRT completely abolished [125I]‐ET‐1 binding in all sites. Other venom peptides did not affect [125I]‐ET‐1 binding. 5. The pattern of [125I]‐SRT receptor binding in rat tissues by in vitro autoradiography was identical to that for ET‐1 receptor binding, and both unlabelled SRT and unlabelled ET‐1 fully competed with [125I]‐SRT for binding. 6. These results provide evidence that SRT binds to the ET receptor in a range of rat tissues. The results suggest that there may be subclasses of ET receptors which can be distinguished by the relative potencies of ET‐1 and SRT at various tissues.